Backflow preventer



FIG. 1 is a top left front perspective view of the backflow preventer showing my new design;

FIG. 2 is a bottom left front perspective view thereof.

FIG. 3 is a bottom right front view thereof.

FIG. 4 is a top right front view thereof

FIG. 5 is a left side view thereof.

FIG. 6 is a top view thereof.

FIG. 7 is a right side view thereof.

FIG. 8 is a bottom view thereof.

FIG. 9 is a front view thereof; and,

FIG. 10 is a back view thereof.

The broken lines shown in the drawings represent portions of the backflow preventer that form no part of the claimed design. 

CLAIM The ornamental design for a backflow preventer, as shown and described. 